The present invention relates in general to fluid control valves, and, more specifically, to performance monitoring of fluid control valves.
Fluid control valves, such as pneumatic valves, perform many industrial functions that involve moving fluid energy from an inlet to one or more outlets and from the one or more outlets to one or more exhaust ports. The fluid energy may be used to control motion of pneumatic cylinders, for example. A valve that performs outside of its normal performance specifications can prevent the system within which it is installed from achieving its required function. This can result in scrap being produced by the manufacturing equipment, damage to the equipment, and production downtime. Production downtime reduces efficiency in the manufacturing process and has direct bottom line costs associated with it. A valve fault (i.e., a condition outside of the valve's normal performance specifications) can result from problems with any number of internal operational components. Components may experience wear or the components may suffer from contamination that becomes introduced during the valve's service life. Eventually, the performance of the valve may degrade to such a degree that it is no longer capable of fulfilling its intended task. However, prior to that point, the valve typically displays diminished performance. Such diminished performance may manifest itself as slower response times or as erratic response. This diminished performance often goes unnoticed during the ongoing manufacturing operations because the valve otherwise continues to operate within acceptable limits and the manufacturing output does not initially suffer.
Functioning of the control valve is usually monitored indirectly based on the influence on the pneumatically-controlled parts of a manufacturing machine and the corresponding machine control system which are monitored according to the production output. As long as the manufactured part is acceptable, then only routine maintenance would be performed on the system components like the control valve. When the production process fails or the produced parts exhibit detectable flaws, the main controller which controls operation of the production process can shut down the system. The production user then troubleshoots the problem based on analysis of the production issue. If the problem can be isolated to the control valve then it can be repaired or replaced.
Besides indirectly monitoring control valve performance, conventional systems often perform direct monitoring of the output of a control valve. Typically, this is accomplished by coupling sensor switches to logic controllers for monitoring valve actuation and deactuation in order to identify if the response was outside of a pre-established parameter. The pre-established parameter is typically based on functional performance of the controlled machine.
Most conventional valve monitoring systems, however, are incapable of addressing the issue of gradually diminished performance nor can they accurately track degradation in a manner to provide any form of prediction of expected remaining serviceable life. International application WO 2006/056214 measures changes in various internal parameters of a control valve and the other pneumatic system components for comparison to pre-established limits. Likewise, European patent 1365159 uses valve monitoring based on stored setpoint values for defining an acceptable switching delay. Due to the foregoing limitations of the prior art, impending faults have not been accurately predicted.